Carbon Pastes and Carbon Paste Electrodes - Electroanalysis with Carbon Paste Electrodes - page 31

.(I-b) Biologically carbon nanotube paste electrodes (CNTP-biosensors) ..Similar.to.CP-biosensors.
in.the.early.1990s.[70],.also.their.CNT-analogues.have.gained.particular.attention.a.decade.
later,.giving.rise.to.a.number.of.new.adaptations.of.already.existing.conigurations.
The.CNTP-biosensors.typically.consist.of.(i).CNTs,.(ii).mineral.oil,.and.an.enzymatic.
system,.that.is,.(iii).enzyme.[364,385,405,433,475],.microbial.cells.[409],.or.biological.tis-
sue.[359],.and.a.(iv).mediator.(or,.instead,.a.binder.capable.of.the.same.functioning.[409]).
(II-a) Carbon paste electrodes modiied with carbon nanotubes and other reagent(s) . that. are.
usually.denoted.as. X(Y)/CNT-CPEs .can.be.split.again.into.two.related.variants.with.the.
modiier. (i). on. the. surface. [393]. or. (ii). admixed—together. with. CNTs—into. the. origi-
nal.graphite.paste.[431]..These.systems.are.also. four-component composites .that.can.be.
obtained.by.mixing,.for.instance,.(1).carbon.powder.+.CNTs.+.hemoglobin.+.liquid.paraf-
in;.(2).graphite.powder.+.CNTs.+.ferrocene.+.mineral.oil.[432].or,.more.speciically,.(3).60%.
(w/w).graphite.powder.+.5%.MW-CNTs.+.20%.PO.+.15%.ionophore.(complexant).[446];.
the.latter.containing.CNTs.due.to.their.beneit.on.the.overall.sensitivity.
And.in.some.applications,.the.respective.mixture.can.be.truly.multicomponential,.which.
was. the. case. of. two. nearly. identical. mixtures. [419,447]. containing. ive constituents :.
(i) 52%-57%. graphite. powder. +. (ii). 5%. MW-CNTs. +. (iii). 20%. PO. +. (iv). 15%-20%.
ionophore. +. (v). 3%. nanosilica.. These. “hyper-heterogeneous”. carbon. paste. composites,.
differing.mainly.in.the.ionofore.used,.were.the.appropriate.ones.of.two.ion-selective.elec-
trodes.developed.for.direct.potentiometric.indication.in.samples.with.complex.matrix.
(II-b) Carbon paste electrodes modiied with carbon nanotubes and an enzyme/mediator system
(CNT-CP-Biosensors) ..According.to.one.selected.report.[381],.this.setup.can.be.of.interest.if.the.
CNTs.serve.as.the.substrate.for.immobilizing.microbial.cells.by.means.of.a.polymer.that.effec-
tively.shuttles.the.electrons.between.redox.enzymes.in.the.cell.and,.at.the.same.time,.promotes.
a.stable.binding.to.the.surface.of.a.common.carbon.paste.completing.the.whole.sensing.system.
.(III) Carbon nanotube paste (Thin) ilm electrodes (CNTFEs) ..In.fact,.these.atypical.conigura-
tions. have. already. been. discussed. in. association. with. new carbon paste electrodes . (see.
Section.2.2.3.and.[127,204,333,334])..It.can.be.briely.repeated.that.the.CPE.is.reduced.to.a.
carbon.paste.ilm.hosting.at.“foreign”.electrode.substrate..Here,.the.four.remaining.exam-
ples.can.be.supplemented.with.other.two.(previously.omitted)..First,.it.is.a.“MW-CNTs.+.
6,7-dihydroxy-3-methyl-9-thia-4,4a-diazaluoren-2-one”.ilm.at.the.surface.of.a.CPE.[439],.
the.second.is. dual carbon-paste-ilm electrode .conigured.as.an. inlaying ultrathin carbon
paste electrode . coated. by. functionalized. (chemically. modiied). CNTs. [446],. when. the.
inner.carbon.paste.layer.has.been.spread.onto.a.nichrome-alloy.substrate.and.the.whole.
coniguration.can.be.schematized.as.“CMCNTs/ut-CP/(Ni-Cr)E.”
With. respect. to. the. construction size ,. a. great. majority. of. both. CNTPEs. and. CNT-CPEs. were.
employed.in.the.usual.macrodesign.(with.the.electrode.diameter.in.the.order.of.millimeters).and.
there.was.only.one.special.series.of.miniaturized.patch-.and.needle-sensors.developed.for. in vivo .
monitoring.and.with.dimensions.balancing.between.mini-.and.microdesign.[377,382,390,396,409].
And.regarding.CNTs-based.CPEs.and.their. compatibility with electrochemical techniques ,.it.
can.be.stated.that.there.are.no.marked.limitations..This.can.be.documented.on.brief.survey.com-
prising.(i).cyclic.voltammetry.(CV;.[360-363,390,398,439]).and.(ii).linear.scan.(sweep).voltam-
metry.(LSV;.[425]),.ramp-modulated.modiications.like.differential.pulse.(DP;.[365,384,416,442]),.
reverse.differential.pulse.(RDP;.[374]),.square.wave.(SW;.[369,376,402]),.and.the.second.deriva-
tive. (2ndDe;. [393,407]). voltammetry,. potentiometric. indication. [399,447],. amperometric. detec-
tion. in. lowing. streams. (FIA;. [367,370,436]),. and. capillary. electrophoresis. [367,370,401],. or.
electrochemiluminescence.detection.[386],.the.latter.two.also.in.a.mutual.combination.(ECL-CE;.
[389])..Furthermore,.useful.information.from.the.characterization.of.CNTs-based.carbon.pastes.
and. the. selected. modifying. systems. could. be. enriched. with. some. speciic. data. obtained. with.